Well honestly I don't know for sure, but my Sprint agreement doesn't mention anything about selling my browsing or location data. I have to take them on faith else I won't be able to have any cellphone service if I don't wish to be tracked.

Correction, you won't be able to have any internet service, period. The fact is, your ISP could be selling information to marketers too. Come to that, your phone company could be selling information about the calls you make, and it doesn't matter if we're talking about a cel phone or a land line. Let's all face facts, in this interconnected world we're living in, we will never have complete privacy. If you want to keep something private, it's best not to even put it out there or, if you absolutely must send it through the internets, encrypt it. Unless you have complete and total control over everything from the origin to the destination endpoints (and you never will) your privacy doesn't exist. It never did, once telephones became widespread.